Donald Trump has indicated at the G 20- meeting that a UK and US free trade deal will happen very quickly to deal with the issue of Brexit. This is, as we will all note, rather different from the attitude of Obama, who said that Britain would be at the back of the queue. There will be those who insist that nothing can actually happen until Britain actually leaves the EU but this is incorrect. Everything can be made ready to happen, that's not a problem:

The US president, Donald Trump, has said he expects a trade deal with the UK to be completed “very, very quickly” and confirmed he will be coming to London, ahead of a bilateral meeting with Theresa May on Saturday.

The point being that there's not really all that much still under discussion. The US and the EU have been working on such a deal for a long time, the UK rules are obviously currently equal to the EU ones. So whatever the deal is can be based upon those other negotiations without too much problem:

Theresa May will attempt to sell the idea of a trade deal with post-Brexit Britain to Donald Trump as the G20 summit moves into its second day.

The Prime Minister will meet the US President on the sidelines of the Hamburg conference.

"We have been working on a trade deal which will be a very, very big deal, a very powerful deal, great for both countries and I think we will have that done very, very quickly."

The point being that this is actually true. Vast amounts of work have been done on the TPIP. Trump is going to want a few changes to it as that's just how he sees his role, the master negotiator. But all the sherpa work, the details, has been done. The UK is already happy with that TPIP. It's really thus just a matter of retyping the header, changing a detail or two and we're ready to go.

It is true that Britain can't bring a US free trade treaty into action before it leaves the EU but there's no problem with doing the negotiating. Given that preparation already done there's no real reason it can't be done quickly.